Moon mysteries

Our solitary satellite has already told us a lot about life on Earth  and it has lots more to say

BySharon J. HuntingtonJune 18, 2002

It was the moon that helped to tell us why dinosaurs disappeared. Scientists studied how impacts might have caused the craters on the moon. Their research helped others theorize how a huge rock crashing into the Earth might have wiped out many forms of life here, including the dinosaurs.

Paul Spudis is a staff scientist and deputy director of the Lunar and Planetary Institute in Houston. He says he feels we still have a lot to learn from the moon.

"Exploring space means opening up thought and imagination," Mr. Spudis says. "We start thinking in new ways and finding solutions to problems here on Earth." He hopes we will decide to go back to the moon soon to learn more.

The moon has been associated with mysterious powers, "green" (unripened) cheese, romance, and alien invaders. Humans have long speculated about its nature and origin. Many early people believed gods lived on the moon or that the moon itself was a god. What else could explain the fact that we saw only one side of it?

The reason we see only one side is that the moon circles the Earth in the same amount of time it takes to rotate on its axis (29-1/2 days). But while the same side always faces us, all parts of the moon face the sun at different times. The moon does have a "far side," which we can never see from the Earth. But it does not have a "dark side" that never gets sunlight. (By the way, you can get a good look at a full moon on June 24.)

We see phases of the moon because sometimes the sunlit side is facing us (a full moon), sometimes only part of the side facing us is lit (gibbous and half moons), and sometimes the side facing us receives almost no light at all (new moon). (See diagram on facing page.)

When Galileo created his first telescope and looked at the moon in 1610, a better study of the moon's surface began. As telescopes improved, so did our maps and understanding of the moon's craters and its "seas" (or maria, in Latin). We know now that these aren't watery oceans but lava-filled plains. Our new knowledge helped refine theories about the moon's origin.

In his book, "The Once and Future moon" (1996), Spudis discusses some common theories and how exploration has helped us narrow down the possibilities.

Some thought the moon broke off from the Earth early in its formation and was trapped in orbit. Others said the moon was a galactic wanderer that came close enough to the Earth to be captured by its gravity. Another theory proposed that a huge rock crashed into the Earth knocking a chunk of it loose that formed into the moon. (This is sometimes called the "big whack" theory.)

When the Apollo astronauts went to the moon, we learned a lot more about its composition. The astronauts left seismographs to measure "moonquakes" and laser reflectors that are still in use. They bounce back laser pulses sent from Earth.

The rocks the astronauts brought back helped determine the age of the moon. They also hinted that the moon had an ocean of magma early in its history. These and other discoveries helped point scientists toward the "big whack" model. More research is needed to say for sure. Lunar research has also given us insights into the Earth, the solar system, and the universe.

So when are we going back to the moon to learn more? Will there ever be colonies there? NASA has no specific plans for moon missions, but it is exploring many possibilities. One is a lunar outpost where scientists could study the moon and the universe and possibly mine elements needed on Earth.

How would you design such an outpost? Consider these factors:

Air: The moon has no air. If you want to breathe, you'll have to bring a supply of air or manufacture it from elements on the moon. It's very expensive to fly anything from Earth, so you'll probably want to find a way to make your own air on the moon.

Food: There's no food on the moon either. But there are basic elements that make up food, including nitrogen, carbon, oxygen, and potassium. Could they be used to supply nutrition or breathable air?

Water: The only water on the moon is in the form of ice. Ice has been detected near both lunar poles. Oxygen could be manufactured from water.

Power: There's plenty of solar power, as long as you're facing the sun. But you'll be in the sun only half the time unless you put your base near one of the poles. A mountain peak at the moon's south pole is so tall that it gets sunlight all year.

Radiation: The universe is filled with radioactivity, which scientists say is harmful to human life. Earth's atmosphere protects us from this cosmic radiation. But you would want radiation shielding at a lunar outpost. One possibility is to dig below the moon's surface and build the outpost under a couple of meters of rock. Water can also be an effective radiation shield, if it's deep enough.

The astronauts who explored the moon had no special radiation shielding, but they were only in space for a week to 10 days. Such short stays are considered safe.

Gravity: The moon is about 2,155 miles across, one-quarter the size of Earth. It has only one-sixth the gravity. If you weigh 60 pounds on Earth, you'd weigh only 10 pounds on the moon. This may sound like fun, but scientists aren't sure what the health effects might be. Exercise may be key.

Location: An outpost on the side facing the Earth would be able to communicate easily with the home planet. But if you want to study the stars, a base on the far side would be free from all the "light pollution" of Earth. Radiotelescopes could also operate there, away from the "noise" of radio and TV signals.

More: A lunar outpost would give humans opportunities to explore the moon, mine its minerals, get a clearer view of the universe, and help us learn more about living in space. What other activities would you plan at your lunar outpost? How would the people there carry them out? Would robots or remote-control machines play a role?

Sketch your own lunar outpost and describe how it would function. Perhaps someday you can compare your idea to the real thing.

Do you know of a 'moon tree' near you?

When Apollo 14 went to the moon in February 1971, Stuart Roosa was the command-module pilot. He orbited the moon while Alan Shepard and Edgar Mitchell explored the surface. Roosa, a former "smoke jumper" (a firefighter who parachutes in to fight forest fires), took some 450 tree seeds with him on the flight. When he returned to Earth, the seeds were planted. The loblolly pine, sycamore, sweetgum, redwood, and Douglas fir trees became known as "moon trees."

These trees were sent all over the world as a living monuments to the Apollo program and to Roosa, who died in 1994. But no complete list was kept of where all the trees were sent. Information on known trees and their locations can be found at this website: nssdc.gsfc.nasa.gov/planetary/lunar/moon_tree.html. But if you know of a moon tree that's not on the list, NASA would like to hear from you. Send your message to dwilliam@nssdc.gsfc.nasa.gov.

The moon takes 29-1/2 days to go around the Earth. The phases of the moon are the result of our observing the moon in different parts of its orbit.

The sun always shines on half the moon, just as it shines on half the Earth. (See diagram below.) Because we can see only the side of the moon that's facing Earth, it appears that the moon is only partly lit sometimes. That's because we can't see all of the lit-up half of the moon.

The moon rises and sets at different times during the month, but don't be fooled: It's the Earth turning, not the moon orbiting, that's most responsible for moonrise and moonset. We spin past the moon much faster than it orbits around us.

One more thing: The moon turns on its axis once every 29-1/2 days, too. That's why we always see the same side of it.